Ask user whether or not to include `partition_id` and `timestamp` before producing

When producing messages to a topic, the extension defaults to sending any "extra" fields aside from `key`, `value`, and `headers`, meaning if the user selects a document that contains `partition_id` and/or `timestamp`, it/they will automatically be sent in the produce request body.

This may be unexpected for some users, but other users may want that behavior to be available, so to try and appeal to both sides we should introduce the following:

Before the 'decide about what schemas to use' QuickPick, scan the record(s) to see if these field(s) are present, and if so, raise a QuickPick:

Submit with provided control fields: [x] Timestamp, [x] Partition ID

(varying which ones mentioned based on presence), and then if user unchecks any, then doctor up the parsed row(s) accordingly, stripping out the keys accordingly.

We can decide at PR time if these two should or should not be checked by default.